JPH0349074A - Inversion preventive circuit - Google Patents

Abstract

PURPOSE:To prevent an inversion phenomenon without causing a deterioration of signal/noise ratio by extracting only the part where a zero-cross point of reformed FM wave is lacking, and making to restore the zero-cross point. CONSTITUTION:An FM signal (b) inputted to a terminal 120 is converted by the 2nd limiter 117 to a signal (c) which the zero-cross point is lacking but the amplitude is uniform on limiting level. On the other hand, the signal (b) is inputted to an HPE 111 wherein the zero-cross point is restored, and formed by the 1st limiter 112 to a signal (e) which the amplitude is uniform on limiting level. The signal (e) is converted to a signal (sh) capable of making a subtraction with the signal (c), passing through an equalizer (EQ) 113. Next, the signal (c) is subtracted 119 from the signal (sh) and formed to a signal having only the lacking zero-cross point, passing through the LPF 114 and a slicer 115, then added 110 with the signal (b) to form a signal (g) by which the zero-cross point is restored after a phase compensation is made in an EQ 116, and the amplitude is made uniform on limiting level by the 3rd limiter 118.

Description

[Detailed Description of the Invention] [Icheon field of business] This invention provides an FM demodulation device in a video signal recording and reproducing device that performs FM modulation on a video signal and records and reproduces the video signal.
The present invention relates to an inversion phenomenon prevention circuit that prevents the inversion phenomenon of an FM demodulated signal by preventing the omission of a zero cross of a reproduced FM modulated wave when a high degree of modulation is recorded.

[Advanced Technology J] Figure 29 is a block circuit diagram of the playback system of the video signal recording IIf production system d, from the LA tape (28) to the video head (
30) is amplified by the amplifier (3I), the RF equalizer circuit (32) (hereinafter referred to as RFEQS path) corrects the frequency a characteristic, and the limiter circuit (33) ( (Hereinafter referred to as LIM circuit), the amplitude is limited and FM demodulated! ! (34) (hereinafter)

FM OEMOD) is used to perform FM demodulation, and a de-emphasis circuit (35) is used to reproduce the video signal.

In a video signal recording and reproducing device as described above.

For example, the video signal is as shown in FIG. 30(d).

In the case of a screen video signal that changes from the black level to the white level, the waveform will be as shown in Figure 30(b), and there is no problem, but in the case of an FM demodulated video signal, the waveform will be as shown in Figure 30(b).
The waveform will be as shown in j4 (a), and the waveform will be as shown in Figure 30 (C).
A problem occurs that causes an inversion phenomenon as shown in .

The cause of such a reversal phenomenon will be explained below.

In a video signal recording/reproducing device, the lower side waves of FM waves are emphasized due to electromagnetic conversion characteristics. When the lower side wave of the FM wave is emphasized compared to the side wave, a zero crossing point is lost.

The LIM circuit (33) in FIG. 29 detects this zero-crossing point, and if a dropout occurs at the zero-crossing point,
A normal FM wave is not output at the output of the LZM circuit (33).If the output of this L I M InJ path (33) is FM demodulated, a normal video signal will not be obtained and a sharp drop in level will occur. The waveform becomes as shown in FIG. 30(a). That is, the lack of zero crossing points causes an inversion phenomenon.

Conventionally, as a reversal phenomenon prevention circuit that prevents such reversal phenomenon, a reversal phenomenon called DL-FM method described in "rNHK Home Video Technology" (by Katsuya Yokoyama, 1 Japan Broadcasting Publishing Association!!), pages 98 to 100, has been used. Prevention circuits are known.

FIG. 31 is a block diagram of this DL-FM type inversion prevention circuit. In the figure, (3B) is a high-pass filter (hereinafter referred to as HPF), and (37) is the first
The LIMH path, (39) is a low-pass filter (hereinafter,
(3) is a phase shifter (hereinafter referred to as E) that adjusts the phase of the signal to be added.
(41) is the second LIMH path.

Next, the operation of the above configuration will be explained with reference to the signal waveform diagram of FIG. 32.

Figure 32 (a) shows the recorded FM wave, and due to the lower side wave emphasis effect caused by this FM wave passing through the electromagnetic conversion system, it is compared to the upper side wave as shown in Figure 32 (b). As a result, the lower side wave is emphasized and the reproduced FM wave is reproduced. Each zero-crossing point of the recorded FM wave is labeled A-J.

In the reproduced FM wave (b) in which the lower side waves are emphasized as described above, zero-crossing points E and zero-crossing points F are missing, and if FM demodulation is performed as is, an inversion phenomenon will occur.

Next, the FMI (b) that passes through the HPF (3B) is reproduced by - The upper side wave is emphasized, and the third wave without missing the zero crossing point is
The signal has the waveform shown in Figure 2 (C), and this signal (e) is the first
The stroke is restricted by the LIM circuit (37) in Figure 32 (
The signal has the waveform d). However, in video signal recording and reproducing devices, the upper side wave generally has a worse C/N ratio, so the signal (d) obtained by emphasizing the upper side wave is a signal slightly shifted from the original zero crossing point due to noise. Also,
There are other causes for the shift in the zero-crossing point, which will be discussed later.

A shift in the zero-crossing point of the FM wave results in deterioration of the S/N ratio after demodulation. For this reason, the above signal (d) is converted to F as it is.
M demodulation results in a reproduced video signal with a poor S/N ratio. On the other hand, the reproduced FM wave (b) is input to the LPF (39), and the lower side wave is emphasized to obtain a signal with a waveform as shown in FIG. 32(e) in which the deviation of the zero cross point due to noise is very small.

This signal (e) is converted to the signal (d) by E Q (38).
) and then the addition! (4G), resulting in a signal with a waveform as shown in FIG. 32(f). This is because the deviation of the zero-crossing point due to noise is smaller than that of signal (d), so a signal such as the one shown in Figure 32 (8) in which the amplitude of signal ('') is limited is compared to the case where signal (d) is demodulated. By demodulating, a reproduced signal with a better S/N ratio can be obtained.

That is, it can be seen that this conventional example is an inversion phenomenon prevention circuit that is capable of restoring the zero cross points E and F, and can generate a demodulated signal with relatively little deterioration of the S/N ratio.

[Problem to be solved by the invention] Since the conventional reversal phenomenon prevention circuit was configured as described above, it is possible to apply HP even to locations where zero cross points are not missing.
Since a signal with a poor C/N ratio that has been suppressed in the low frequency range by F (3f) is added, the zero crossing point is shifted due to noise, resulting in a problem of deterioration of the S/N ratio.

Furthermore, a shift in the zero-crossing point occurs even when there is no noise at all and when the frequency characteristics of the FM transmission system are not flat. In particular, in the DL-FM type reversal phenomenon prevention circuit, the output of L P F (39) and the output of HP F (
3B) and the output passed through the first LIM circuit (37), the frequency characteristics of the FM transmission system change, causing a shift in the zero-crossing point. Such a shift in the zero cross point causes a change in the frequency characteristics of the demodulated 1S image signal or causes distortion.

Furthermore, in the DL-FM type reversal phenomenon prevention circuit, a change in the addition ratio changes the degree of the effect of suppressing the video phenomenon. Therefore, there is a problem in that the frequency characteristics of the demodulated video signal change or distort depending on the degree of the suppression effect of the one-inversion phenomenon.

This invention was made in order to solve the above-mentioned problems, and it is an inversion prevention circuit that can sufficiently restore the zero cross point and minimize the deterioration of the S/N ratio of the FMa (jl signal). The purpose is to provide

[Means for Solving the Problems] The inversion phenomenon prevention circuit according to the present invention is applicable to ++T live FM signal 1) which suppresses the low frequency range and limits the range by one width, and llf live FM signal to which only the 41IJ edition is applied. The inversion phenomenon prevention circuit according to the invention set forth in claim 2 is characterized in that it is configured to restore the zero-crossing point of the FM wave by calculating only the signal with a wide pulse width by calculating the input signal. Compare the output signals of the means for suppressing the lower side wave component of the FM wave and distinguishing between positive and negative and the means for determining the positive and negative as is the input FM wave, and if the time period in which the two output signals differ is long, the output signal will be proportional to that time. The reversal phenomenon prevention circuit according to the invention set forth in claim 3 is characterized in that it is configured to extract a pulse with a width of The system is configured to subtract the reproduced FM wave with a missing zero-crossing point from the reproduced FM wave, extract only the signal of the missing zero-crossing point, and add the signal 1) of the extracted zero-crossing point to the original reproduced FM wave. It is characterized by

[Function] According to the present invention, the means for extracting a signal with a wide pulse width corresponds to detecting a place where a zero-crossing point is missing, and has the effect of restoring a zero-crossing point only at the place where the zero-crossing point is missing. conduct.

Further, according to the invention described in claim 2, by extracting a signal with a wide pulse width, only the place where the zero cross point is missing is detected, and the zero cross point is restored only at the place where the zero cross '+A is missing. This makes it possible to suppress the one-inversion phenomenon without deteriorating the S/N ratio.

According to the invention amended in Claim A [3], by extracting the signal of only the missing zero-crossing point and adding this beat signal to the missing zero-crossing point of the reproduced FM wave,
The zero-cross point is sufficiently restored to prevent the reversal phenomenon, and an FM signal with a sufficient S/N ratio can be obtained.

[Embodiment of the Invention] An embodiment of the present invention will be described below based on the drawings.

First Embodiment FIG. 1 is a block diagram showing the configuration of an inversion phenomenon prevention circuit according to a first embodiment of the present invention.
11) is HP F, (132) is the first limiter,
(117) is the second limiter, (118) is the limiter of A3, (113) and (118) are EQ, (114) is LPF, (+15) is a circuit for removing small amplitude signals (hereinafter referred to as slicer). ), (119) is a subtractor, (+1
0) is an adder, (12G) is an input terminal for the 1G raw FM signal, and (121) is an output terminal.

Next, the operation of the first embodiment having the above configuration will be explained with reference to the pIS2 diagram showing the process of waveform change.

The FM signal input to the terminal (120) is as shown in Fig. 2 (a).
The zero-crossing point of the FM signal shown in
This is a signal as shown in Fig. Jj2 (b). The input signal (b) is input to the second limiter (117), where the zero crossing point (x) is missing as shown in ff$2 diagram (C), but the limiting level ( C5), (
Lfl) can be changed to a signal with uniform amplitude.

On the other hand, the input signal (b) is input to HP F (111), where the zero crossing point (X) is restored as shown in FIG. 2(d). The restored signal (d) at the zero crossing point (X) is input to the first limiter (112) and the amplitude is adjusted to the limiting levels (C7) and (C8) as shown in FIG. 2 (11). It becomes a complete signal.

This zero crossing point (signal + where RI is restored and the amplitudes are aligned) (e) is passed through E Q (133), and the phase relationship is aligned with the above signal (C) where the amplitudes are aligned.

The signal (C) is changed into a signal (Sh) that can be subtracted from it.

Then, when the output signal (C) of the second limiter (117) is subtracted from the output signal (sh) of the above E Q (113) using the subtracter (+19), the output signal (sh) of the above EQ (113) is obtained. Since the S/N ratio is good, the signal becomes a signal in which high-frequency components of frequencies outside the divination range are added to the signal shown in FIG. 2(f). The output signal of the above subtraction 'J (IIJ) is passed through the LPF (114) which blocks high frequency components outside the divinion range, and the LPF (114)
By passing the high frequency components outside the divination range that have been attenuated to minute signals by the slicer (115) having the human output characteristics shown in FIG. Figure 2 (f) with only points
The signal shown in is obtained.

The output of this slicer (+15) is passed through an EQ (11B) for phase compensation so that it matches the phase relationship with the input FM signal (b), and then the input FM signal (b) and the adder (11
Figure 2 (g
) can be obtained. And the above adder (
110) output signal (g) to a third limiter (118)
As shown in Figure 2(h).

n1NI at limiting level (C9), (LIO)
Arrange the IJ.

In the manner described above, the zero-crossing point can be fully restored. In addition, HP F (111) and the first limiter (
Since the aJ& signal obtained by The S/N ratio does not deteriorate unnecessarily.

Note that E Q C1C113) A114 is added to compensate for the phase relationship during addition and subtraction, so if the phase relationship matches during addition and subtraction, it is not necessarily arranged as shown in Figure 1. Alternatively, they may be arranged and configured as shown in FIG. 4, for example.

Further, the LPF (114) may be a BPF as long as it passes frequencies within the divinion.

Furthermore, L P F (114) or slicer (
(5) may be omitted if the S/N ratio can be obtained at a practically acceptable level.

According to the first embodiment configured as above, from the signal whose zero-crossing point has been restored by the 2HPF and the limiter, the signal obtained by applying the limiter to the input signal is subtracted n, and the zero-crossing point is restored only in the portion where the zero-crossing point is missing. Since the configuration is configured to extract a signal only for the purpose of reproducing and adding this extracted signal to the original reproduced FM signal, the zero cross point is restored to 1-minute without unnecessarily changing the S/N to Q. be able to. This makes it possible to prevent the reversal phenomenon while improving the S/N ratio.

Second Embodiment FIG. 5 shows the reversal phenomenon vj according to the second embodiment of this emission 151.
This is a block diagram showing the configuration of the +l- circuit, in which (211) is a bandpass filter (211) that suppresses low frequencies.
(hereinafter referred to as BPF), (212), (214)
, (210) is a limiter circuit, (213) is B P F
Equivalent to (211)? ! a first delay device with a delay of (2
15), the subtractor (21111) is L P F , (2
+7) is a slicer that removes small amplitude signal components, (21B
) is the second 21! l! : Container, (220) is a subtractor.

Next, the operation of the second embodiment having the above configuration will be explained with reference to FIG. 6, which shows the process of waveform change.

Figures 6(i) and (j) show the same waveforms of the recorded FM wave and (reproduced FM wave) as in Figures 32(a) and (b), and the waveforms of the reproduced FM wave.
The M wave (j) is input to B P F (211), first and second slow SLl'= (213), (218). First delay device (2+3) and limiter circuit (214)
As a result, the waveform t) shown in FIG. 6(k), which has very little deviation from the original zero-crossing point, can be obtained. This signal (k)
By FM demodulating the S/
Although the N ratio is good, a one-inversion phenomenon occurs.

On the other hand, due to B P F (2+1), a signal with the waveform shown in FIG. 6 (!L) is obtained, which is deviated from the original zero-crossing point but has no zero-crossing point, and by the limiter circuit (212), the waveform shown in FIG. 6 is obtained. (s) waveform signal is lost.

Next, the signal (1) is subtracted from the signal (k) by the signal generator (215), resulting in a signal with the waveform shown in FIG. 6 (+1). Among the waveforms of this signal (n), the narrow pulse (
nl) is a pulse generated due to a shift in the zero-crossing point, and is a wide pulse (n2) between zero-crossing point E and zero-crossing point F (172, which is the reciprocal of the instantaneous frequency).
A pulse with a width close to ) is a pulse caused by a missing zero crossing.

That is, the waveform of the signal (n) is a mixture of a pulse (fll) generated due to noise and a pulse (n2) generated due to lack of a zero cross. Therefore, the signal (
If we can extract the pulse (n2) generated due to the missing zero-crossing point from the waveform n), we can create an inversion phenomenon prevention circuit that only restores the zero-crossing of the reproduced FM wave and does not degrade the S/N ratio ( can do.

L P F (218) and slicer (217) are circuits for extracting the pulse (n2) generated due to missing zero-crossing points. L P F (218) generally has an integral characteristic, and Figure 7 (L), (M), (M
) The pulse signals with different widths as shown in (0) in the same figure, respectively.

It becomes a pulse signal with the waveform shown in (P) and (Q), and is applied to each pulse IIJPI-P3.

The amplitude hl-h3 changes.

The pulse width U;-(0) whose pulse width is converted into an amplitude by LPF (218) is extracted by the slicer (2+7), where only the pulse of the amplitude l- is extracted. In other words, the output 0 of L P F (218) is shown in Figure 6 (Q
), and of this signal (0), only the portion having a larger amplitude than the slice level (Lth) indicated by the - dotted chain line (L12) is extracted. This extracted signal is: 52
Ff raw F whose phase is adjusted by the delay device (218)
By subtracting it from the M signal ('') and limiting the amplitude with the limiter circuit (210), a signal with the waveform shown in FIG.
Since F is a restored signal and a signal with a poor C/N ratio is not always added as in the conventional case, the S/N ratio of the demodulated signal does not deteriorate.

Furthermore, since the pulse is applied only to the missing zero cross, the frequency characteristics of the reproduced video signal are not changed, and the effect of suppressing the inversion phenomenon is extremely large.

In addition, when B P F (211) is formed by a sine type filter (219) with good phase linearity, the first
The 'M spreader (213) is not necessary, and the configuration as shown in FIG. 8 may be used.

The sine filter (219) has a similar configuration to an FIR filter, and includes delay devices (219a) and (219b).
and coefficient units (219c), (219d), (219e)
and an adder (211N), and by changing the coefficient ratio, you can freely create 111! Numerical characteristics can be provided, and phase matching can be easily performed.

Incidentally, in the configuration shown in FIG. 8, the adder (221) is.

Coefficients of the sine filter (219) and subtractor (215)
FA calculation may be performed so that the zero crossing is restored using the signal (02) extracted by a subtracter according to the determination of the positive or negative sign 1) of ).

Further, if reflective type ones are used for the 'M delay devices 219a) and (219b), the delay device can be configured with one delay device.

Third Embodiment FIG. 9 is a block diagram showing the configuration of a reversal phenomenon prevention circuit according to a third embodiment of the present invention. The structure shown in FIG. 9 is used instead of the container (221).

In FIG. 9, (322), (323), (32
4) is a converter, which outputs an H level when the input signal t) is above a certain level, and outputs an L level when the input signal is below a certain level;
(325) and (32B) are exclusive OR circuits.

Next, regarding the operation of the third embodiment of the above JA configuration, the first θ
This will be explained with reference to the diagram.

FIG. 10(i) shows a recording FM signal, and ('') shows a reproduced FM signal, which is assumed to have the same waveform as FIGS. 6(i) and (j). When the threshold levels of comparators (322) and (323) are set to ACOV, B P
F (211) and further comparator (32
3), it becomes a signal with a waveform as shown in Figure 1θ (r) with the zero crossing restored (the zero crossing point is shifted from the original position), and the signal is passed through the first delay device (213) and comparator (322). The signal that has passed becomes a waveform signal with zero cross points E and F missing, as shown in FIG. 10(q).

When the exclusive OR circuit (325) performs the exclusive OR of the signals (q) and (r), a signal having the waveform shown in FIG. 1θ (j) is obtained. This signal (j) is a signal corresponding to the signal shown in FIG. 16 (II). When this signal (1) is passed through the LPF (218), it becomes a signal with the waveform shown in FIG. 10 (1). Comparator (324) threshold level (L1
2) to the level indicated by the - dotted chain line, the comparator (32
The output signal of tjS10 has the waveform shown in figure (u), and the second
Delay! 1 (21B), the signal (
q) and the signal (u) using an exclusive OR circuit (32B), it is possible to obtain a signal with a waveform that reproduces the zero-crossing points E and F shown in Figure 1θ (ma). .

By performing such digital processing, the limiter circuit (21G) in the embodiments of FIGS. 5 and 8 can be omitted.

Alternatively, the configuration shown in FIG. 11 using a delay device (327) and an AND circuit (32B) may be used as a means for extracting only the signal with a wide pulse width from among the signals shown in FIG. 1O(g). .

FIG. 12 is a signal waveform diagram of the main part of the embodiment of fJS11. The signal shown in FIG. 10 (s) is the same as the signal shown in FIG. 12 (s), and this signal (s) is , τ5eci! by the delay device (327) in FIG. +! extended 12th
The signal will be as shown in the figure (Cao). Logical product circuit (328) -t't! logic Flu of signals (s) and (w). : Ruto.

The signal becomes as shown in Figure 12 (Ten), and τse of the signal (w)
0, which can extract pulses wider than c.
The delay time τ may be set to 172 or less, which is the reciprocal of the Nk high instantaneous frequency.

Note that the means for extracting a pulse wider than τsec is as follows:
The structure is not limited to these methods, but may also be constructed using, for example, a monostable multivibrator or a flip-flop.

The optimal delay amount of the delay device (218) in FIG. 11 is the propagation delay of the exclusive OR circuit (325) and the AND circuit (328), and l/2 of the delay result τsec of the delay device (327). It is the sum with a certain τ/2 S el C.

Fourth Embodiment As a means for restoring the zero-crossing point, the t52 embodiment shown in FIGS. 5 and 8 restores the zero-crossing point by linear operations called addition and subtraction, and In the example, the zero crossing point was restored by pool algebra calculation, but in the fourth embodiment shown in FIG.
This is a JA configuration that uses non-linear calculation to restore the zero-crossing point by dynamically adjusting the hump rate level. FIG. 14 is a signal waveform diagram in the case of the f54 embodiment.

In FIG. 13, the configuration up to the slicer (217) and the delay device (218) is the same as in the first embodiment, so the same reference numerals are given to the corresponding parts and detailed explanation will be omitted.

Next, the operation of the fourth example of E-class acid structure will be explained.

This will be explained with reference to FIG.

As explained in the first embodiment, when the input signal is the reproduced FM wave shown in FIG. 14 (D), the output signal (02) of the slicer (217) becomes as shown in FIG. 14 (0). That's right. Let this signal (02) be the Humbalate level,
The comparator (420) has a second delay Lf 2! (2
18), if the phase-matched signal (j) is input, the first
A signal with the waveform shown in Figure 4 is output. In other words,
Using the signal shown in FIG. 14(0),
When the FMI generated signal shown in is input, it is H level,
In the opposite case, the L level is output, so at the zero cross point E, F1il, the signal (a) in FIG.
o2) is larger.

The output of the comparator (420) becomes L level, resulting in a signal (
You can get more.

Note that the comparator (420) is a MIN circuit.

Even if a MAX circuit is used, 4I can be achieved in IBJJJ.

Also, the second aspect of this invention. The third and fourth embodiments may be combined appropriately.

For example, the configuration of BPF using the sine type filter (219) in Fig. 8 and the comparator (322) in Fig.
, (323), gates (325), (328), and a delay device (327) in combination with the pulse extraction circuit 4111&, as shown in figure ff515, an inversion phenomenon prevention circuit that can prevent inversion phenomena in a digital circuit is created. can be configured.

Fifth Embodiment FIG. 16 is a block diagram showing the configuration of an inversion prevention circuit according to a tJ%5 embodiment of the present invention. In the same figure,
(511) is the first delay device, (512) is the lower band P
HPF suppressing IIl & min, (513) is tjIJ2
(510 is a first positive/negative discrimination circuit, and these positive/negative page discrimination circuits (513) and (514) detect, for example, when the input signal is greater than ACOV, the 3H level, A
It is smaller than COV! ! It is configured to output L level.

(515) is an exclusive OR circuit, (ste) is a second delay device, (517) is an AND circuit, (518) is a sign control circuit, (519) is a third The retarder, (520) is an adder, - the above exclusive OR circuit (515) and the second 'j! Spreader (51 fl)
and AND circuit (517) and code 'M11 circuit (518)
A third delay device (519) and an adder (520) add an inversion phenomenon occurrence detection pulse that adds a pulse with a width proportional to the degree of zero-crossing missing to the input FM wave to the portion where the zero-crossing point is missing. It constitutes a circuit (521).

Next, regarding the operation of the fifth embodiment of the L structure acid, ill
This will be explained with reference to the signal waveform diagram shown in Figure 's17.

Figures 17(a) and (b) are the same waveforms as Figures 32(a) and (b), and Figure 16 is the reproduced FM wave (b) in Figure 17.
This is an inversion phenomenon prevention circuit when input is:

The first delay: 1I (511) has the same delay time as HP F (512), and this! The output of the delay device (511) of
), the H level is output when the amplitude is larger than the center value, and the L level is output when the amplitude is smaller than the center value, so a signal like ff117ffJ(b) is output.

On the other hand, since the HP F (512) outputs a waveform signal that is shifted from the original zero-crossing point but does not have any zero-crossing points, when its reliability is input to the first positive/negative discrimination circuit (510), , the signal shown in FIG. 17(i) is output.Then, the signal shown in FIG. 17(h) and il
Each signal in Figure 7 (+) is input to the exclusive OR circuit (515), and the exclusive OR of both signals (h) and (i) is taken to detect the missing zero-crossing point in the FM wave. A zero value as shown in FIG. 17 (D) is output so that the H level is reached only where there is a deviation between the zero cross point and the zero cross point.

The signal 1t output from the exclusive OR circuit (515)
t(D, the time at H level is relatively long, that is, (FM wave) II & high instantaneous frequency) If this is taken into account, the zero-crossing point of the FM wave can be restored.

Therefore, the delay of R2! (51B) in Figure 17 (
The waveform of D is delayed to obtain the signal shown in FIG. 17(k). By inputting both the signals in Fig. 17 (j) and Fig. 17 (k) to the logical Jg product circuit (517) and extracting pulses only where the zero-crossing point is missing, the signal shown in Fig. 17 (1)
obtain a pulse signal.

In order to add such a pulse signal, it is necessary to consider the polarity. In other words, when you want to restore the zero-crossing point in Figure tjS17 (h), the location where the zero-crossing point is missing is at H level, and at this H level, a pulse is generated with negative polarity with respect to the input FM wave (b). , and conversely, the location where the zero cross point is missing is
When the level is reached, a pulse of positive polarity may be added. This operation is performed by the code M control circuit (518).

That is, the code control circuit (518) converts the pulse signal shown in FIG. 17 (text) into the pulse signal shown in FIG. 1 (520), the 17th
It is possible to obtain the signal shown in Figure (!I).

This signal -(fl) is a waveform in which the zero-crossing point of the input FM wave (b) has been restored, and furthermore, the signal on the upper side wave side with a poor C/N ratio is not constantly added.

It is possible to perform demodulation with a good S/N ratio, and
There is no change in frequency characteristics after demodulation.

In other words, even if the 1 reversal phenomenon suppression effect is changed.

No change or distortion occurs in the frequency characteristics of the video signal after demodulation.

In addition, FIG. 18 shows a specific example of the configuration of the sign control circuit (518), and FIGS. In FIG. 19, the relationship between resistance (R) and ('e) is H>>re.

Further, the third delay 1m (519) is the code control circuit (
518), and as shown in Fig. 21, E is installed after the third delay device (519).
Q (522) may be arranged to perform some equalization, that is, the first delay device (522) may be arranged to perform some equalization.
2) and HP F (512), respectively.
If the positive and negative signs do not match, and the time period during which the positive and negative signs do not match is relatively long (maximum instantaneous frequency of FM wave) x 2 or more, that is where the zero cross point is missing. All you have to do is add a pulse with a width proportional to the degree of the dropout to the input FM wave at that point.The purpose of adding a pulse with a width proportional to the degree of the dropout is to restore the zero cross dropout as faithfully as possible. This method has the advantage that the zero crossing can be restored more faithfully than adding a pulse with a constant width or a differential waveform with a constant time constant created by a 41 stable multi-by-break.

Sixth Embodiment FIG. 22 shows how to prevent the reversal phenomenon according to the 1$6 embodiment of the present invention.
t: l! II I#i is a block diagram showing the configuration of I#i. In the same figure, the difference from the fifth embodiment shown in FIG. Rather than adding the input FM wave to L
The point is that it is added to the signal after amplitude limiting through the IMH path (523), and the other a components are the 16th
54, the same reference numerals are given and the explanation thereof will be omitted.

According to the sixth embodiment having the configuration as shown in FIG. 22, it is possible to remove and add the envelope fluctuations that the FM wave undergoes during the transmission process.

In addition, the H shown in the fifth and sixth embodiments of
P F (512) may be used as a BPF, or when emphasis is placed on phase characteristics, B P F (550) having a phase linear characteristic as shown in FIG. 23 may be used.

In FIG. 23, (551) and (552) are delay devices.

(553), (554), (555) are in charge! l vessel,
(55B) is an hl calculator, each coefficient unit (55ff),
The numbers entered in (554) and (555) are the input coefficient ratios, and if you want the added output gain to be 1, -1/2
, 1, -1/2, and the B P F (550) with such a configuration is converted into the HP F (51
2) By using K instead, a filter with phase quadrature characteristics can be obtained by 4iJ.

Although not shown, the delay device (551) in FIG.
, (552) are replaced with reflective ones, the configuration shown in FIG. 23 can be obtained using one filter.

In addition, in order to obtain a wide pulse, in the fifth embodiment, the second delay group (5111) and the AND circuit (517) are used.
However, as shown in FIGS. 24 to 27, L P F (55B) and slicer (559)
When the time constant of the LPF (558) is constant, the peak value of the pulse width after passing through the LPF depends on the pulse width. By configuring the pulse width to be cut off, it is possible to eliminate a pulse having a width corresponding to a signal below the certain threshold of 4n.

In addition, in the fifth embodiment of the "bipod", two positive/negative discrimination circuits (5
13), an exclusive OR circuit (515) was used as a means to compare the outputs of (5th), but other circuit configurations may also be used.For example, it may be configured with a subtracter (55?). have the same effect. However, when using the subtracter (557), when the positive/negative discrimination circuit (513) of wS2 is H and the first positive/negative discrimination circuit (510 is L), the pulse is in the positive direction, and the second When the positive/negative discrimination circuit (51:l) is L and the first positive/negative discrimination circuit (510 is H), it can be realized with one subtractor so that the pulse is in the negative direction. 518) can be omitted.In addition, when comparing using a subtracter in this way, in order to extract a wide pulse, L P F (55
8) and a slicer (559), but it is also possible to use a second Mi W (5111) and logic.

Note that the above-mentioned configurations may be freely combined, for example, the configuration shown in FIG. 24! B P F (55G) having the phase linear characteristic shown in Fig. 1623, a subtracter (557) as a means for comparing the outputs of two positive/negative discrimination circuits (513) and (514), and one for extracting a wide pulse. LP F (558) and slicer (559) in 1
1.

In addition, FIG. 25 shows iE positive/negative discrimination circuits 513) and (514).
), when the configuration shown in FIG. 19 or 20 is used, B P of the phase linear characteristic L
F (550), subtractor (557) and L P F
(558) and a slicer (559), and the structure shown in FIG. 25 also produces the same effects as in the embodiment shown below. This is because when using FMa, pulse count type FMia equipment only focuses on zero cross information, so the positive/negative discrimination circuit (513)
, (514), zero cross information is input to F
This is because there is no difference from the M wave, and therefore the effect remains the same even if 11x is added to the output of the positive/negative 21 separate circuit (513) or added to the input FM wave.

Further, FIG. 26 is a block diagram showing the configuration of a modified example of the reversal phenomenon prevention circuit according to the sixth embodiment of the present invention,
The positive/negative discrimination circuit (output of 510 and the second positive/negative discrimination circuit (510)
The output of the subtracter (557), which is compared with the output of the subtracter (513), is passed through the LPF (55B) and the slicer (559) to extract only wide pulses, and this pulse is passed to the second positive/negative discrimination circuit (513). 51:l) output signal by E Q (
522) is configured to be added to the equalized signal.

Moreover, FIG. 27 is a block diagram showing the configuration of another modification of the inversion phenomenon prevention circuit according to the 886 embodiment of the present invention, in which the input FM wave is equalized by the E Q (522) and the LIM circuit (523 ), the extracted wide pulse is added to the amplitude-limited signal.

FIG. 28 shows a specific example of the configuration of the slicer (559), and FIG. 28 (A) shows a one-sided slicer whose output is max (E2.El + sl). The figure (B) shows a double-sided slicer, and its output is WaX (E2.
El + el ) +min (lE3.El +
el) There is.

As described above, according to the present invention, only the missing zero-crossing point of the reproduced FM wave is extracted and the zero-crossing point is restored, so that the deterioration of the S/N ratio can be prevented. It is possible to suppress the one-reversal phenomenon without causing any harm. Also, to restore the zero-crossing point only in the missing part of the zero-crossing point.

Since the frequency characteristics of the reproduced video signal are not related to the effect of preventing the reversal phenomenon, there is also the effect that even if the reversal phenomenon is prevented, the frequency characteristics of the reproduced video signal do not need to be changed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an inversion phenomenon prevention circuit according to a first embodiment of the present invention, FIG. 2 is a signal waveform diagram of each part explaining the operation of the first embodiment, and FIG. 3 is an input/output diagram of the slicer. 4 is a block diagram showing the configuration of a modification of the first embodiment; FIG. 5 is a block diagram showing the configuration of a reversal phenomenon prevention circuit according to the second embodiment of the present invention; FIG. A signal waveform diagram of each part explaining the operation of the second embodiment, Fig. 7 is the LP
FIG. 8 is a block diagram showing the configuration of a modified example of the second embodiment; FIG. 9 is a block diagram showing the configuration of a reversal phenomenon prevention circuit according to the third embodiment of the present invention; FIG. 10 is a signal waveform diagram of each part explaining the operation of the third embodiment, FIG. 11 is a block diagram showing the configuration of a modification of the third embodiment, and FIG. 12 is a diagram of the first! Signal waveform diagram of the main part of the figure,
FIG. 13 is a block diagram showing the configuration of an inversion prevention circuit according to a fourth embodiment of the present invention, FIG. 14 is a signal waveform diagram of the main part explaining the operation of the fourth embodiment, and FIG. Block diagram of a configuration combining the embodiment and the third embodiment, first
FIG. 6 is a block diagram showing the configuration of an inversion phenomenon prevention circuit according to a fifth embodiment of the present invention, FIG. ff117 is a signal waveform diagram of the main part explaining the operation of the fifth embodiment, and FIG. FIGS. 19 and 20 are circuit diagrams of specific configuration examples of the positive/negative discrimination circuit, and FIG. 21 is a block diagram showing a configuration of a modification of the fifth embodiment.
FIG. 22 is a block diagram showing M41& of the inversion phenomenon prevention circuit according to the sixth embodiment of the present invention, and FIGS.
The figures are block diagrams showing configurations of modified examples of the fifth embodiment and the sixth embodiment, respectively. Figures 28 (A) and (B) are circuit diagrams showing specific configuration examples of the slicer, Figure 29 is a block circuit diagram of the reproduction system of the video signal recording and reproduction apparatus, and Figure 30 is for explaining the inversion phenomenon. 31 is a block diagram showing the configuration of a conventional DL-FM inversion prevention circuit, and FIG. 32 is a signal waveform diagram of the 3rd generation
FIG. 2 is a signal waveform diagram illustrating the operation of FIG. 1; (110), (221), (520)...adder,
(111), (512)...HP F, (11
2), (11?), (118), (210), (212
), (214)...Limiter, (115), (21
7), (559)...Slicer. (1111), (215), (220)...M calculator,
(211), (550)... B P F , (
2111), (55+1)...LPF,
(513), (514) ... Positive/negative discrimination circuit,
(515) ---exclusive disjunction, path. (518)...Sign control circuit, (521)...Reversal phenomenon occurrence detection pulse addition circuit. Note that the same reference numerals in Figure 1 indicate the same or corresponding parts.

Claims (3)

[Claims] (1) a low-frequency suppression means for suppressing the lower side wave component of the input FM wave; a first amplitude-limiting means for amplitude-limiting the output signal of the low-frequency suppression means; and a second amplitude-limiting means for amplitude-limiting the input FM wave. and calculation means for calculating the phases of the output signal of the first amplitude limiting means and the output signal of the second amplitude limiting means to generate a pulse signal representing the missing portion of the zero crossing point. , means for extracting only a pulse signal with a wide pulse width from among the output pulse signals of the calculation means;
A reversal phenomenon prevention circuit comprising: waveform correction means for restoring the zero-crossing point of the input FM wave based on the extracted pulse signal. (2) a low frequency suppression means for suppressing the lower side wave component of the input FM wave; a first positive/negative determination means for determining the sign of the output signal of the low frequency suppression means; By comparing the output signals of the second positive/negative determining means and the first and second positive/negative determining means, it is determined whether or not the time during which both output signals are different is long. 1. A reversal phenomenon prevention circuit comprising: pulse adding means for adding a pulse having a width proportional to the time to an input FM wave. (3) A bandpass filter that restores the zero-crossing point by inputting the reproduced FM wave with the missing zero-crossing point, a first amplitude limiting means that makes the amplitude of the output signal of this band-pass filter uniform, and the zero-crossing point that is missing. Played FM
a second amplitude limiting means for aligning the amplitudes of the waves; a subtracter for subtracting the output signal of the second amplitude limiting means from the output signal of the first amplitude limiting means; and reproduction of the output signal of the subtracter and the original. 1. An inversion phenomenon prevention circuit comprising: an adder for adding FM waves; and third amplitude limiting means for aligning the amplitudes of output signals of the adder.